1,1-Dichloro-1-fluoroethane, prepared by fluorination of Vinylidgne chloride (A. E Feiring, J. Fluorine Chem., 1979, 14(1), 7-18)or of 1,1,1-trichloroethane (U.S. Pat. No. DE 2,137,806), contains, as impurities, chlorinated or chlorofluorinated unsaturated compounds which are undesirable when 1,1-dichloro-1-fluoroethane is used and must therefore be removed. Among the unsaturated impurities, the most harmful is vinylidene chloride, whose boiling point (31.7.degree. C.) is too close to that (32.degree. C.) of 1,1-dichloro-1-fluoroethane for its separation to be possible by distillation.
Among the various techniques already proposed for removing the unsaturated impurities (in particular vinylidene chloride ) present in 1,1-dichloro-1-fluoroethane, there may be mentioned:
liquid phase photochlorination (U.S. Pat. No. 4,948,479 ) or vapour phase photochlorination (publication WO 92/10452)
chlorination in the presence of a Lewis acid catalyst (publication EP 0,420,709)
absorption of the impurities on a carbonaceous molecular sieve (U.S. Pat. No. 4,940,824) or on active charcoal (U.S. Pat. No. 4,950,816)
catalytic hydrogenation (U.S. Pat. No. 5,105,035)
treatment with concentrated H.sub.2 SO.sub.4 (publication JP 04-99737 ).
It has now been found that the unsaturated impurities, in particular vinylidene chloride, may be removed by photooxidation.